Another way to look at it is to note that (2(n+1)) is the difference, where n is the sequence number of the value. So for n=1, 2(n+1)=4, for n=2, 2(n+1)=6, etc. So to find the next number in the sequence, simply multiply the sequence number + 1 by 2 and add that value to the value of the number at sequence number n; value of n+1 = 2(n+1) + value at n. So if the value of n=1 is 2, the next value should be 2+2(1+1) = 6. And it is! If n=2 and the value at 2 is 6, 6+2(2+1) = 6+6 = 12. Works again!